Colour bleaching catalysts for the silver dyestuff bleaching process



3,443,947 COLOUR BLEACHING CATALYSTS FOR THE SILVER DYESTUFF BLEACHING PROCESS Rudolf Mory, Dornach, and Alfred Oetiker, Fribourg,

Switzerland, assignors to Ciba Limited, Basel, Switzerland, a Swiss company No Drawing. Filed Nov. 16, 1965, Ser. No. 508,156 Claims priority, application Switzerland, Nov. 20, 1964, 14,974/64 Int. Cl. G03c 7/02 US. Cl. 96-53 7 Claims ABSTRACT OF THE DISCLOSURE Process for the production of coloured photographic images by the silver dyestuff bleaching method. The silver dyestuff bleaching operation is carried out in the presence of a catalyst containing a pyrazine ring and sulfonamide groups. These catalysts yield particularly good results as they are free from acid groups and auxochromic groups. Clean whites at points of high exposure are obtained.

It is known that the production of coloured photographic images by the silver dyestuff bleaching process depends on the fact that organic dyestuffs, particularly azo dyestuffs, are destroyed by image silver in suitable baths. These baths generally contain a mineral acid, e.g., hydrochloric acid, or a strong organic carboxylic'acid, potassium bromide, and a compound capable of forming silver complexes, for example thiourea. Theoretically, one azo group is reduced by four silver atoms, with the formation of colourless amines. However, the azo dyestuffs show considerable differences in behaviour during this reduction process, particularly in the different periods of time required for the reduction to the colourless state. Furthermore, the silver dyestuff bleaching process is mostly completed without the total amount of image silver present being utilised, but instead is interrupted after a certain time and after only a part of the silver has been consumed. As a result bleaching continues, in the case of a prolonged bleaching period, in those places where metallic silver is still present, so that a weakening of the half tones is to be feared, particularly at places where the optical colour density is low.

It is also known that for bleaching many azo dyestuffs it is necessary to have a catalyst which evens out the bleaching time of the various dyestuffs as far as possible, and which permits bleaching to a pure white where necessary. 2,3-dimethylquinoxaline, 2,3-diaminophenazine, 2- hydroxy-3-aminophenazine or anthraquinone sulphonic acid have for example been suggested as bleaching catalysts, and have in part been used with success. The catalysts are usually added to the silver dyestuff bleaching bath or incorporated into the photographic colour layer. It is however also known to add the catalysts to a bath which precedes the silver dyestuff bleaching bath. Thus a series of catalysts and various possible ways of using them are already available. Nevertheless there are always difficulties in the use of the catalysts. In particular it is difiicult to catalyse the colour bleaching process in such a way that the different dyestuffs of a multilayer material are bleached to a similar extent in the same time. Thus for example a certain catalyst may shorten the bleaching time of the yellow and cyan dyestuff without however. influencing the bleaching time of the magenta dyestuff. Another catalyst may, conversely, be effective only with regard to the magenta dyestuff whereas no effect is achieved on the yellow and cyan dyestuffs. It is however States Patent ice not only a question of adjusting the bleaching periods, but also of adjusting the gradation, so that curves should be obtained which are as straightlined and parallel as possible in a diagram showing logarithmically the dependence of the optical density on the exposure.

A further disadvantage of the bleaching catalysts hitherto known is that these compounds, in as much as they are effective at low concentrations of about 1-10 milligrarnmes per litre, as for example, 2,3-diaminophenazine or 2-hydroxy-3-aminophenazine, possess a pronounced colour of their own. This can produce an unattractive tinting of the gelatine or of the film carrier. In contrast thereto, the known colourless catalysts, for example 2,3-dimethylquinoxaline, exert a considerably weaker effect and therefore have to be used in larger amounts.

It is therefore desirable to have available as large a number as possible of effective colourless catalysts in order to be able to bleach the most varied azo dyestuffs in the film layers in as nearly as possible the same time and to the same colour gradation. Sometimes a single catalyst is sufficient, but it is also possible to use several simultaneously at suitable concentrations. Furthermore, as mentioned above, a catalyst may also be added to the bath which precedes the silver dyestuff bleaching bath, and one or more other catalysts may then be brought into play in the silver dyestuff bleaching bath. Such a combination of colour bleaching catalysts can also be useful in the reduction of disazo dyestuffs, in which the reduction clearly takes place in two stages via a difiicult intermediate reduction stage. With some of these dyestuffs, in particular cyan disazo dyestuffs, or azoxyazo dyestuffs, e.g., the known symmetrical disazo dyestuff made from tetrazotised, 3,3 dimethoxy-4,4'-diaminodiphenyl and 1-amino-8-hydroxynaphthalene-2,4-disulphonic acid, the colour bleaching process using the known catalysts, particularly at pH-values greater than 2, takes place in such a manner that only the first azo group is decomposed and a monoazo dyestuff, which is most frequently violet in colour, remains in the film layer. For this reason it is desirable to have colour bleaching catalysts which particularly catalyse the decomposition of the monoazo dyestuff so produced, since the latter has a very disturbing effect particularly in the white parts of the image.

This invention is based on the observation that compounds which are free from acid water-solubilising groups, and which contain at least one pyrazine ring with at least one fused aromatic ring and at least one sulphonamide group, may be used as colour bleaching catalysts in the silver dyestuff bleaching process, with particularly good resulfis.

The compounds to be considered are thus those which contain one or more rings of the formula III result, in which R and R" denote hydrocarbon residues which are only connected with one another via the pyraz ine ring. These pyrazine compounds do not contain any acid water-solubilising groups such as carboxylic or su-lphonic acid groups. They are also preferably free from auxochromic groups, i.e., hydroxyl and amino groups bound to aromatic carbon atoms. Generally speaking, they should be as colourless as possible.

Advantageously compounds are used which fulfil the conditions referred to and which correspond to the formula R1 R3 I I 5 N al R N a and to phenazines of the formula which may contain further rings fused to the aromatic 6-membered rings A and/or A Thus the pyrazine compounds for example advantageously contain at least one monocyclic benzene group fused to the pyr-azine ring, or a naphthalene group. A sulphonamide group is attached to at least one of these aromatic groups via its sulphur atom.

The sulphonamide groups required in the compounds to be used according to the invention may be an H NO 'S group or, preferably, further-substituted sulphonamide groups, i.e., those that have secondary or tertiary nitrogen atoms, For example, compounds with further-substituted sulphonamide groups, which in addition to the nitrogen atom bound to the sulphur atom also contain at least a basic tertiary nitrogen atom or a heterocyclic group having :a ring nitrogen atom, have proved particularly valuable. Compounds in which the sulphonamide group has a further residue containing a pyrazine ring should also be mentioned.

Some characteristic groups of compounds which meet the conditions just quoted to a greater or lesser extent, and which may be used as dyestuff bleaching catalysts, are listed below:

(1) Compounds of formula in which R; and R have the significance indicated and X denotes a sulphonamide group having a secondary or tertiary nitrogen atom bound to the sulphur atom; R and R may be for example phenyl or alkyl groups, preferably methyl groups.

(2) Compounds of formula in which R and R have the significance indicated and R denotes a heterocyclic group having a-ring nitrogen atom, e.g., a. pyridine group or an aliphatic group with a basic nitrogen atom.

(3) Compounds of formula in which X denotes a sulphonamide group with a secondary or tertiary nitrogen atom bound to the sulphur atom, preferably a group of formula [in which R has the significance given under (2)] and Y denotes a hydrogen or chlorine atom. The 'y-di-n-b utylaminopropylsulphonamide group may be mentioned as an example of group X.

(4) Compounds of formula X E I \I X in which X has the significance indicated. X may for ex ample be a sulphomethylamide group.

(5) Compounds of formula 11 Nj:Ra R

R N/ NIH-02S in which R R R and R have the significance indicated, and each, for example, may represent a methyl group.

The compounds to be used as dyestuff bleaching catalysts according to the invention may be produced by known methods. Thus for example the compounds of Formula 7, in which R and R each denote a methyl group, may be produced by the reaction of l,Z-diaminonaphthalene-6-sulphonamides with diacetyl. The 1,2-diaminonaphthalene-6- sulphonamides needed as starting materials for this are obtained by coupling a suitable diazo compound, e.g., diazobenzene, in an acid medium, with a 2-aminonaphthalene-6- sulphonamide, and reducing the o-aminoazo dyestuff thus obtained with sodium dithionite.

Depending on solubility and ability to diffuse in gelatine, it may be appropriate to incorporate the catalysts to be used according to the invention into one or more layers of a photographic material for the silver dyestutf bleaching process or to utilise them in a treatment bath.

Those catalysts possessing suflrcient solubility in such baths, e.g., in the colour bleaching bath or in a bath which precedes this, for example the developer, a hardening bath, a stopping bath, or a special bath after the fixing bath, are with advantage used in such baths and here again yield particularly valuable results.

In other respects these dyestuff bleaching catalysts may be used in known manner. They are able to accelerate the bleaching of many azo dyestuffs to an extraordinary extent even in very small amounts, particularly if they are added to the dyestufi bleaching bath. For example, the addition of 0.001 to 0.100 g. of catalyst per litre of a dyestutf bleaching bath of the conventional composition, e.g., a bath containing hydrochloric acid, potassium bromide and thiourea, suffices to produce a pronounced effect.

In the example which follows the parts and percentages are by weight and the temperatures are given in degrees centigrade, unless otherwise stated.

EXAMPLE A photographic material having three colour layers comprises on a cellulose acetate film, a silver bromide emulsion sensitive to red, containing a cyan dyestulf of formula above this an empty gelatine separating layer, and then a silver bromide emulsion sensitive to green, containing a magenta dyestuff of formula (13) NH: 8N=NQ -E OH I i H 03S H038 After a further separating layer there follows a layer containing a yellow filter dyestuif or colloidal silver acting as a yellow filter. On top of this there is a silver bromide layer containing the yellow dyestuff of formula 0 Ha CH3 and optionally a covering layer. All these layers may be hardened by means of a halotriazine compound, e.g., 2,4-

mCHS

in 10% hydrochloric acid. The bleaching time is 8 to 15 minutes. After a brief washing with water, the residual image silver is converted into silver halide in the usual manner, in a bath containing copper sulphate, hydrochloric acid and potassium bromide. Finally the film is S OzH HO washed with water, fixed with a 10% solution of ammonium thiosulphate, and once again washed with water.

A positive image of the master with cleanly bleached dyestuffs at points of high exposure, is obtained.

Instead of the cyan dyestufr of Formula 12 the layer which is sensitive to red may also contain the cyan dyedichloro-6-phenylamino-1,3,5-triazine-3'-sulphonic acid. 65 stuff of formula H2CCH2 HC-HN OH SOaH 7 and instead of the dyestuif bleaching catalyst of Formula 15 dyestuff bleaching catalysts of formulae may be used in the manner indicated above.

The preparation of dyestuif bleaching catalysts of formulae 15, 17 and 18 is explained below using the compound of Formula 15 by way of example:

34 parts of the dyestuff prepared in the usual manner by coupling diazotised aminobenzene with 2-aminonaphtalene-fi-sulphomethylamide are purified by recrystallization from dilute alcohol and introduced into 500 parts by volume of 30% ethanol. The mixture is heated to boiling under reflux. 19.8 parts of 88% sodium dithionite and 20 parts by volume of 30% sodium hydroxide solution at a time are then added four times at quarter-hourly intervals. The reduction is complete after heating for a total of 1 hour. The pale yellow solution obtained is diluted with a 1,000 parts by volume of cold water and treated with 30 parts by volume of 35% hydrochloric acid. After cooling the separated crystals are filtered and washed with water until the filtrate is neutral. In order to purify it, the product is recrystallised from ethanol. The l,Z-diamiononaphthelene-fi-sulphomethylamide melts at 170-172 C.

25.1 parts of this diamine mixed with 200 parts by volume of alcohol and 9.5 parts by volume of diacetyl are heated to boiling for minutes. After cooling, the condensation product is filtered, washed with cold alcohol, and purified by recrystallisation from ethanol.

The pale yellowish quinoxaline derivative of Formula melts at 238239 C.

We claim:

1. In a process for the production of colored photographic images by the silver dyestutf; bleaching method the improvement which comprises carrying out the silver dyestuii bleaching operation in the presence of a compound as a dyestuif bleaching catalyst which corresponds to the formula in which R and R each represent a member selected from the group consisting of an alkyl, aryl, cycloalkyl and heterocyclic group and X represents a sulfonamide group having a secondary or tertiary nitrogen atom.

2. In a process as claimed in claim 1 the improvement which comprises carrying out the silver dyestufi bleaching operation in the presence of a compound as a dyestuif bleaching catalyst which corresponds to the formula l-cni in which X represent a sulfonamide group having a secondary or tertiary nitrogen atom.

3. In a process as claimed in claim 1 the improvement which comprises carrying out the silver dyestuif bleaching operation in the presence of the compound of the formula N CH3 as a dyestulf bleaching catalyst.

4. In a process as claimed in claim 1 the improvement which comprises carrying out the silver dyestufi bleaching operation in the presence of the compound of the formula K CK.

Ha -H26 N CH3-CH3N III-02S- as a dyestufi bleaching catalyst.

5. In a process as claimed in claim 1 the improvement which comprises carrying out the silver dyestufi bleaching operation in the presence of the compound of the formula 9 10 ing catalyst 21 compound which corresponds to the from the group consisting of an alkyl, aryl, cycloalkyl formula and heterocyclic group and X represents a sulfonarnide Rl group having a secondary or tertiary nitrogen atom.

5 References Cited N UNITED STATES PATENTS 3,318,700 5/1967 Andreau et a1 96-53 I. TRAVIS BROWN, Primary Examiner. 10 X US. Cl. X.R. in which R and R each represent a member selected 96-20 

